umlaut

An assimilatory process whereby a vowel is pronounced more like a following vocoid that is separated by one or more consonants.

The umlaut process (as above) that occurred historically in Germanic languages whereby back vowels became front vowels when followed by syllable containing a front vocoid (e.g. Germanic lūsiz > Old English lȳs(i) > Modern English lice).

A vowel so assimilated.

The diacritical mark ( ¨ ) placed over a vowel when it indicates a (rounded) front vowel

Diaeresis

“Naïve takes an umlaut as it's pronounced as two syllables.”

To place an umlaut over (a vowel).

To modify (a word) so that an umlaut is required in it.

“an umlauting vowel”